1. Field of the Invention
This invention concerns compliant electrical contacts for fuel cell use to create, adjust and distribute internal forces and loads to optimize electrical connection and contact area to increase fuel cell performance. In a number of embodiments, an array of metal springs of different shapes and configurations contact the adjacent electrode.
2. Description of the Related Art
Fuel cells are energy conversion devices that use hydrogen (the most abundant element on earth) as a fuel, and oxygen, usually from the air, as an oxidant to create electricity through a chemical conversion process, without combustion and without harmful emissions. The voltage and current output of a fuel cell system depends on the number of cells in the stack, total active surface area and efficiency. The basic process, for a single cell is shown in FIG. 1.
Traditional fuel cell stacks 1, see FIG. 2, are made of many individual cells 2, see FIG. 3, which are stacked together. For the proper operation of the fuel cells the hydrogen gas fuel must be sealed inside the fuel cell and separated form the gaseous oxidant (air or oxygen). In some fuel cells, cooling is required because of the heat generated during normal operation. This heat is commonly removed from the fuel cell sacks by means of liquid cooling, typically using water as a coolant. The ability to achieve the required hydrogen and oxidant gas sealing as well as the liquid coolant sealing and to maintain intimate electrical contact between the bipolar plates 8 and the electrodes 9 has traditionally been accomplished with the use of relatively thick and heavy xe2x80x9cend platesxe2x80x9d 3, 4 with the fuel cell stack 5 held together by heavy tie-rods or bolts 6 and nuts 7 (or other fasteners) in a xe2x80x9cfilter-pressxe2x80x9d type of arrangement. (See FIGS. 2 and 4). Disassembly and analysis of fuel cell stacks built by traditional and other methods reveals evidence of incomplete electrical contact between bipolar separator plates (BSPs) 8 and the membrane electrode assemblies (MEAs) 9, which results in poor electrical conduction, lower cell performance, often along with evidence of gas and liquid leakage.
The traditional method of assembly of Proton Exchange Membrane (PEM) fuel cells requires several parallel and serial mechanical processes that must be accomplished simultaneously for each individual cell, see FIG. 3.
The Membrane Electrode Assembly (MEA) 9 must be sealed to the Bipolar Separator Plates (BSPs) 8 at each plate/MEA interface, via a gasket 10A and 10B. The fuel, oxidizer and coolant manifolds 11, 11A and 11B are all required to be sealed at the same time during fabrication as the MEA is sealed to the BSP. The BSPs 8 must be in intimate electrical contact with the electrode assembly 9, across its entire surface area, at all times for optimum performance.
As the traditional fuel cell stack 1 is assembled, each individual cell (layer) 2 must seal, manage gasses and liquid, produce power and conduct current. Each cell relies on all the other cells for these functions. Additionally, all seals and electrical contacts must be made concurrently at the time of assembly of the stack. (See FIGS. 2 and 3).
The assembly of a traditional PEM cell stack which comprises a plurality of PEM cells each having many separate gaskets which must be fitted to or formed on the various components is labor-intensive, costly and generally unsuited to high volume manufacture due to the multitude of parts and assembly steps required.
The traditional construction method does not allow for testing or evaluation of the individual cells before they are assembled into the stack. If there is leakage or a performance problem with a single cell or group of cells in an assembled stack, then the entire stack has to be disassembled to correct the problem. This is very expensive and time consuming.
Some patents of interest are listed below. U.S. Pat. No. 5,683,828 discloses metal platelet fuel cells production and operation methods. U.S. Pat. No. 5,858,567 discloses fuel cells employing integrated fluid management platelet technology. U.S. Pat. No. 5,863,671, discloses plastic platelet fuel cells employing integrated fluid management. U.S. Pat. No. 6,051,331 discloses fuel cell platelet separators having coordinate features. These four U.S. patents describe conventional fuel cell assembly.
U.S. Pat. No. 6,030,718 describes a proton exchange membrane fuel cell power system. In the figures of this patent, particularly its FIG. 12 and following, component 202 is described as a xe2x80x9cbiasingxe2x80x9d assembly, namely a plurality of metal wave springs which cooperate with the cathode cover and impart force to the adjacent pressure transfer assembly 203 through a rigid pressure distribution assembly 204. These springs are not described or claimed as contacts.
Other of general interest includes, for example, European Patent 446,680 and U.S. Pat. Nos. 5,338,621, 5,328,779, 5,084,364, 4,445,994, 5,976,727, 5,470,671, 5,176,966, and 5,945,232. All of the references, patents, standards, etc. cited in this application are incorporated by reference in their entirety.
The above discussion shows that existing fuel cell technology can be improved with modification in the design and fabrication of fuel cell components, and in the assembly of the units. The present invention of compliant electrical contacts provides such improvements.
The present invention concerns a single compliant electrical contact or an array of independently-acting compliant electrical contacts within a fuel cell electrode. This invention improves fuel cell operation by providing substantially uniform internal load distribution to effect uniform electrical contact across the conductive surface.
In one embodiment of the invention, the compliant electrical contacts are metal springs, which can take a number of forms, including but not limited to an inverted V (or U), Z, S or omega shape. The contacts can be connected to a conducting base plate or BSP in a number of ways, including electrical, mechanical or metallurgical connections, or combinations thereof.
The contacts can be arranged in a regular pattern, providing substantially uniform distance between contact surfaces or they can be arranged in an irregular pattern, providing a non-uniform distance between contact surfaces.
The contacts can be made of many conducting substances, including but not limited to alloys of iron, copper, gold, silver, platinum, aluminum, nickel, chromium, and combinations thereof.